Both industry and research communities have the need for the controlled generation of liquid microdroplets with uniform characteristics. The contents of droplets can e.g. be molten organics, polymers and metals. The produced droplets can e.g. be converted to gelled polymer beads or solidified metal beads used for drug delivery, tissue engineering, compounding, coating and proportioning in pharmaceutical, biomedical, plastic and cosmetic industry. The two major requirements for droplet generation typically are high throughput and monodisperse in size distribution. Additional requirements for pharmaceutical and biomedical applications include contamination free, and thus a disposable part (for the part in contact with the flowing liquid) will be preferable.
Conventional microfluidic platforms, fabricated with Polydimethylsiloxane (PDMS), Poly(methyl methacrylate) (PMMA), glass or silicon for generating single or double emulsions, are disposable. However such platforms cannot run at high throughput, e.g. more than 1 milliliter per minute in terms of the flow rate of disperse phase.
In the case where oil is used as the carrier phase and surfactants are employed to stabilize the droplet formation process and to avoid the coalescence of droplets, additional separation processes are required to retrieve crosslinked droplets or beads from the oil followed by a thorough washing to remove the surfactants adsorbed on the gelled droplets. Such separation processes typically involve surfactants, which is not preferred for many applications, e.g. for cells or bio-molecules encapsulation process.
Additionally, the need of several pressure controlled or syringe pumps for multiphase emulsion forming on chip also can make the scale-up very costly. Thus, in industry, conventional microfluidic platforms are currently not preferred, instead high-throughput methods, such as ink jet printing, piezo tubing ejection, vibration of chamber, are employed for the droplet formation. In droplet generators such as ink jet printing, piezo tubing ejection and vibration of chamber, the fluid contacts the print head, piezo vibrator or the vibration chamber. None of these parts are disposable since they are either expensive or cannot be easily separated from a complicated and integrated system. When change-over (change of dispensing liquid) is frequent, a thorough cleaning of liquid-contacting portions of the system is necessary. Such cleaning process is extremely tedious when the contamination control is strict, e.g. for the process of bio- or drug encapsulation.
There is therefore a need to provide a droplets/beads generation method and apparatus, that seek to address at least one of the above problem.